x86: Reduce clock calibration time during slave cpu startup

[karo-tx-linux.git] / arch / x86 / kernel / tsc.c

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index db483369f10be5c07bfe8564a1a073c34ffb22fb..490fb330be87bae0239f523cfd20286e33edf9f6 100644 (file)
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -995,3 +995,23 @@ void __init tsc_init(void)
        check_system_tsc_reliable();
 }
 
+#ifdef CONFIG_SMP
+/*
+ * If we have a constant TSC and are using the TSC for the delay loop,
+ * we can skip clock calibration if another cpu in the same socket has already
+ * been calibrated. This assumes that CONSTANT_TSC applies to all
+ * cpus in the socket - this should be a safe assumption.
+ */
+unsigned long __cpuinit calibrate_delay_is_known(void)
+{
+       int i, cpu = smp_processor_id();
+
+       if (!tsc_disabled && !cpu_has(&cpu_data(cpu), X86_FEATURE_CONSTANT_TSC))
+               return 0;
+
+       for_each_online_cpu(i)
+               if (cpu_data(i).phys_proc_id == cpu_data(cpu).phys_proc_id)
+                       return cpu_data(i).loops_per_jiffy;
+       return 0;
+}
+#endif